PROJECT SUMMARY While significant progress has been made in identifying de novo gene mutations linked to autism risk, much less attention has been paid to environmental risks and the extent to which these risks cause autism pathology in susceptible individuals. Environmental factors, including gestational exposure to pyrethroid pesticides and valproic acid, are implicated in risk for autism. Prenatal exposure to pyrethroids is also linked to risk for developmental delay and attention deficit hyperactivity disorder (ADHD)?one of the most common neurodevelopmental disorders. However, these environmental risks were identified retrospectively, after a large number of people were exposed. Thousands of chemicals are registered for use in the environment, and humans are potentially exposed to many of these chemicals to varying degrees, including chemicals in plastics and building materials. We currently lack a way to systematically evaluate which environmental-use chemicals have the greatest potential to harm the developing brain. The inability to identify environmental threats to the brain early?before they cause disease?represents one of the major public health challenges of our time. This challenge is particularly relevant to autism, which now affects 1 in 59 individuals in America, and where heritability studies indicate that genetic and environmental factors contribute to autism risk. Our research program is guided by the hypothesis that ?candidate? environmental risks for autism and other neurodevelopmental disorders can be identified rationally, by identifying chemicals and mixtures that target molecular pathways implicated in these disorders. Our long term goals are to 1) identify environmental-use chemicals and mixtures that target molecular pathways implicated in neurodevelopmental disorders. These studies will utilize primary human neural progenitor cells (phNPCs), primary neurons, and endpoints that are compatible with high-throughput screening. 2) Assess real world exposure to these chemicals/mixtures. If environmental sampling and biomonitoring data are not available for these chemicals/mixtures, we will work with a network of Environmental Health Science (EHS) researchers to collect these data. 3) Evaluate exposure risk in vivo using wild-type and CRISPR/Cas9-engineered mice that model human de novo autism-linked mutations. We will prioritize chemicals/mixtures that a) impact one or more phNPC/neuron assay endpoints, b) are verified exposure risks to humans, and c) enter the placenta and/or developing brain following maternal exposure. While the specific projects will evolve over time, we plan to initially focus on individual and joint exposures to pyrethroids and strobilurins?a new class of fungicides that inhibits mitochondria. Both chemical classes impair neuronal functions and co-occur in the home environment. We will evaluate the extent to which prenatal exposure to these and other prioritized chemicals and mixtures exacerbate brain and behavioral phenotypes associated with autism and other neurodevelopmental disorders across the lifespan.